FISHERY BULLETIN: VOL. 78, NO. 2 



8.1 cm fetus would be late June or early July, and 

 for the 61 cm fetus would be early May. 



Thus, although the data are few, there is a con- 

 vincing consistency indicative of a calving season 

 for this population in early summer (May-July). 



PHYSICAL MATURITY 



Physical maturity was judged on the basis of 

 examination of the epiphyseal suture in one of the 

 midthoracic vertebrae and noting whether a car- 

 tilaginous plate was present (open), absent but 

 with the epiphyseal line still visible (closed), or 

 absent with all trace of the epiphyseal suture 

 obliterated (fused). The suture was examined on a 

 cut surface at least 1 cm deep, and generally on a 

 median section of a whole centrum. Closure of the 

 suture takes place last along the periphery of the 

 epiphyseal plate, and a shallow cut can frequently 

 be misleading. As can be seen in Table 2, males 

 reached physical maturity at about the same size 

 as sexual maturity (with the exception of 504447, 

 which as noted earlier, was probably an abnormal 

 individual). Females, however, reached physical 

 maturity considerably after sexual maturity, at a 

 length of about 196 cm and a weight of about 61 kg. 



EXTERNAL MORPHOLOGY 



External measurements were taken in the 

 manner outlined by Norris (1961), at the time the 

 animals were picked up from the beach, using a 

 steel tape graduated in centimeters. Numbers in 

 parentheses in the text refer to the numbered 

 measurements as defined in that paper. In the 

 following discussion, relative dimensions are with 

 respect to the total length of the individual, and 

 are expressed as the means of the individual di- 

 mensions divided by the individual total lengths 

 (Table 3). Figure 2 shows the long slender rostrum 

 and a pigmentation pattern characteristic of this 

 species. 



Sexual dimorphism in the external measure- 

 ments was most apparent in the relative length of 

 the rostrum (snout to apex of melon (3)). This di- 

 mension was about 7% larger in females for the 

 total sample, but was less in the adult and 

 neonatal samples. Perrin (1975) found the same 

 sexual difference in the sample of S. longirostris 

 which he examined from the Pacific. 



The other anterior body measurements which 

 are taken from the tip of the snout show sexual 

 differences of a lower relative magnitude, due to 



358 



Table 3. — External measurements on Florida spinner dolphin 

 expressed as individual dimensions divided by individual total 

 lengths. For these purposes animals with a total length >195 cm 

 were considered adult. Numbers in parentheses refer to Norris 

 (1961) for definitions of the measurement. 



inclusion of the rostral length as a component of 

 these dimensions. We should then expect, if no 

 other factors were active, that all measurements 

 containing rostral length would be proportion- 

 ately greater in females, and all those not contain- 

 ing rostral length would be proportionately 

 smaller. In this particular sample, however, the 

 variation is such that these differences are not 

 apparent in most cases. 



The position of the center of the genital slit, as 

 determined by the measurement from the tip of 

 the snout to the genital slit (13), differs between 

 males and females, with the center of the slit being 

 farther posterior in females. The difference 

 amounts to a relative increase of about 8% in this 

 measurement in adult females when compared 

 with adult males. This particular sexual differ- 

 ence seems to be true of cetaceans in general. 



Girth at the anus (23) relative to total length is 

 about 11% greater in adult males. This is corre- 

 lated with development of a postanal keel in adult 

 males as described by Perrin (1972, 1975). 



The relative width of the flukes (34) was 5-8% 

 greater in males in the adult, total, and neonatal 

 samples. Although the variation in this character 

 renders this statistically insignificant in this 

 sample, the same sort of difference was found by 

 Perrin (1975) in his Pacific samples, suggesting 

 that it is a real difference. The relative height of 

 the dorsal fin (32) was 7% greater in males in the 

 total sample. Here again, the variation renders 

 the difference statistically insignificant. There is a 

 possible indication that the flippers are relatively 

 larger in females, but the difference is slight 



